Method for automatic fabric inspection

ABSTRACT

Fabric such as textile material is automatically inspected at high speed by diffraction of light techniques. The fabric is moved through a plane and irradiated with monochromatic light of given cross sectional area sufficient to encompass a large number of warp and fillings making up the fabric. The diffraction pattern developed after the beam has passed through the fabric is detected and various regions of this diffraction pattern are processed to provide data indicative of the quality of the fabric. The major regions involved in the diffraction pattern include the developed central lobe and first order side lobes along orthogonal axes normal to the directions of the warps and filling threads of the fabric.

This invention relates to an improved method for automatic fabricinspection particularly useful in the textile industry.

BACKGROUND OF THE INVENTION

It is conventional practice for quality control purposes to inspectfabric manufactured in textile mills.

At the present time, there are two basic techniques for such inspection.First, light is transmitted through the fabric and the intensity of thelight measured. Variations in the intensity will indicate variations indensity of the fabric material. Second, a reflective technique isemployed wherein fabric is irradiated with light and the reflected lighttherefrom is analyzed.

Another technique known in the art for analyzing various materials isthat of utilizing monochromatic light and developing diffractionpatterns. For example, a single wire filament can be so analyzed as tosize and form by irradiating the filaments with monochromatic light andanalyzing the developed diffraction pattern. See, e.g., U.S. Pat. No.3,659,950 issued May 2, 1972. However, so far as we are aware, nofeasible technique has been developed prior to the present invention fora rapid analysis of fabric utilizing diffraction pattern techniques.

BRIEF DESCRIPTION OF THE PRESENT INVENTION

With the foregoing in mind, the present invention contemplates animproved method for fabric inspection particularly applicable to qualitycontrol of fabric manufactured in textile mills.

More particularly, we have discovered that diffraction pattern analysistechniques may be utilized in the high speed inspection of fabric frommills by the irradiation of the fabric with a monochromatic light beamof a given cross-sectional area sufficient to encompass a large numberof the warp and fillings making up the fabric. In this respect, ourmethod differs from known methods of diffraction analysis of materials.

In addition to the basic step of encompassing a large number of warp andfilling threads, the developed diffraction pattern is in the form of atime sequential pattern in a single output plane. Thus, the fabric iscaused to move through a given plane while being irradiated with themonochromatic light and the sequential developed pattern at the outputplane is continuously analyzed.

Many different types of defects in fabric can readily be detected byprocessing various regions in the output plane of the diffractionpattern and the fabric graded in accordance with the output datafurnished by this processing.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the method of this invention will be had byreferring to the accompanying drawings in which:

FIG. 1 is a highly schematic perspective view of the basic componentsfor automatic fabric inspection in accord with this invention;

FIG. 2 is a perspective view of the developed time sequentialdiffraction pattern at the output plane of the detector of FIG. 1;

FIG. 3 is an enlarged view of one of the side lobes of the diffractionpattern of FIG. 2;

FIG. 4 is a greatly magnified view of a fabric area under analysisillustrative of a first type of defect; and,

FIG. 5 is a view similar to FIG. 4 illustrating a second type of fabricdefect.

DETAILED DESCRIPTION OF THE INVENTION

Referring first to FIG. 1, there is shown typical fabric material 10from a textile mill which is caused to move downwardly as indicated bythe arrow in a vertical plane P. Any suitable fabric transport systemcan be provided such as a supply roll 11 and take-up roll 12 for thefabric 10.

The basic components for carrying out the method include a monochromaticlight source such as a laser 13 for irradiating the fabric with acollimated beam formed by a collimating lens 14. The irradiated area isindicated at Af and is of sufficient cross-sectional area to encompass alarge number of the warps and fillings of the fabric.

Typical fabrics may have from 40 to 100 threads (that is, warps orfillings) per inch. Thus, the expression "large number" as used hereinwould typically be from 40 to 100 or more threads per inch. However, thetechnique is workable for a number as low as 25 but in most instances,the number of warps or fillings per inch would exceed this minimumnumber. The diameter of the beam from the collimating lens 14, in turn,may be between 1 and 2 inches.

As is evident from FIG. 1, the monochromatic light beam is directedtowards one side of the fabric 10 preferably in a directionsubstantially normal to the plane of the fabric. The light beam afterpassing to the other side of the fabric is focussed by transform lens 15onto a detector 16, a diffraction pattern being developed in a singleoutput plane 17.

In order that the entire area of the fabric 10 be inspected, the area Afis scanned across the width of the fabric as indicated by the phantomlines at the same time that the fabric 10 is moving downwardly. Thus,the pattern developed in the plane 17 of the detector will be a timesequential pattern for all of the successive areas irradiated by themonochromatic light beam.

FIG. 2 schematically illustrates the developed diffraction patternwherein there is provided a central lobe C with various first order sidelobes. The side lobes of importance in this diffraction pattern arethose lying on axes X--X and Y--Y which axes are oriented in directionsnormal to the directions of the warp and filling threads of the fabric,respectively.

With respect to the foregoing, if the warp constitutes the verticalthreads in the fabric as viewed in FIG. 1 and the filling the horizontalthreads, the side lobes W1 and W2 along the X--X axis of FIG. 2 resultsfrom the warps whereas the side lobes F-1 and F-2 along the Y--Y axisresult from the fills. As stated, it is principally these first orderside lobes along the X--X and Y--Y axes as described which are importantalong with the central lobe in providing an indication of the overallquality of the fabric.

The processing of the diffraction pattern to grade the fabric involvescollapsing each of the lobes into a sheet of energy by an anamorphiclens system. Each of these sheets of energy (or one dimensional sidelobe pattern) is then processed by its own individual photo detectorarray which converts the light intensity into electrical form. Each ofthe sequential electronic signals is then processed to make good v.defective decisions.

Thus, still referring to FIG. 2, various regions of the diffractionpattern are individually processed, typical regions being indicatedwithin the broken line enclosures R1, R2 and R3.

Considering first, by way of example, the side lobe W1 and the region R1there is illustrated in FIG. 3 a cross section of the lobe in solid linewhich results when the fabric is "good." In the event there is a defectin the warp, the height and shape of this lobe is changed usually by alowering of the side lobe peak and a broadening of its overall shape. Aspecific defect is illustrated in FIG. 4, wherein there is a doublethread (two closely spaced warp) designated defect #1. Referring back toFIG. 3, the solid line lobe would degenerate into a size and shapeindicated at W1'. This defect is referred to as a "double thread"defect.

A second type of defect is illustrated in FIG. 5 and is referred to inthe art as a "slub." This defect is indicated as defect #2 and mightresult from foreign material on one of the warp.

Referring back again to FIG. 3, such a defect would typically result ina degeneration of the "good" solid line curve for the lobe to the dashedcurved W1".

It will be evident from the foregoing, that by simply comparing theheights and shapes of the side lobes to given references, the desiredoutput data can be obtained and a grade count accorded the particularcross sectional area of the fabric being inspected. An important one ofthe given references for comparison purposes is that of the height andshape of the central lobe. This central lobe in itself provides valuableinformation as to major defects since its intensity will vary withchanges in density of the overall fabric material. In addition, however,by utilizing the central lobe as a comparison reference for the sidelobes, the analysis of the side lobes will be essentially independent ofchanges in the transmissivity of the fabric.

The method of this invention also includes processing steps involvingthe comparing of the distances between the centroids of the side lobeswith given references to determine spacing between the warps and betweenthe fillings of the fabric. These distances are indicated by the smallletters a and b in FIG. 2 and serve as an indication to enable thenumber of warps and the number of fillings per inch to be determined.

In the preferred method of this invention, the given references forcomparison purposes are provided from the mean value of a history ofamplitude and shape comparisons of the side lobes. For example, if thenumber of occurrences in any of the amplitude quantitization levels isfurther than + or - one standard deviation from its mean value, adecision of a defect would be made. Such histograms are preferablydeveloped as noted, relative to the central lobe so that the decisionscan be made independently of the fabric transmissivity.

Further, in the preferred embodiment of this invention a statisticalhistory of the height and shapes of the side lobes is formed in anadaptive manner, the history for a current decision being related onlyto the last few samples tested.

From the foregoing, it will be appreciated that not only are individualsequentially graded local areas of the fabric through which the beampasses carried out, but in addition, the individual grades of such localareas over a given large area of the fabric can be totalled and anoverall grade assigned to a large area as to its quality.

The comparisons of the shapes and heights of the side lobes with givenreferences can actually be carried out by simply observing the developeddiffraction patterns on a screen positioned in front of the detector 16of FIG. 1. In this case the pattern is visually observed and compared tothe pattern developed by a "good" fabric. Photographs can be taken ofthe pattern on the screen and compared with previous photographs.

Preferably, however, the first order side lobes are squeezed by a lensand detected in a photo-diode linear array. One such type of diodedetector is shown and described in U.S. Pat. No. 3,937,580 issued Feb.10, 1976 to Harvey Lee Kasdan one of the co-inventors in thisapplication. Another type of photo-detector array which could serve toprocess the diffraction pattern of this invention is shown and describedin U.S. Pat. No. 3,689,772 issued Sept. 5, 1972. In this latter respect,the basic method of fabric inspection in accord with this invention hasbeen carried out using a photo-detector as shown in U.S. Pat. No.3,689,772 with portions masked off to provide a linear array so thatside lobes along either the X--X or Y--Y axis could be individuallyanalyzed by appropriately orienting the unmasked portion of the arrayparallel to the particular axis under investigation.

From the foregoing description, it will be evident that the presentinvention has thus provided a greatly improved method for the rapidinspection and grading of fabric from textile mills and can be carriedout in a manner to provide substantially more information as to thefabric quality than has been possible with prior art methods involvingsimple light transmissivity of the fabric or reflection characteristicsfrom one side of the fabric.

What is claimed is:
 1. A method of automatically inspecting fabriccomprised of warp and filling threads to determine the quality of thefabric, including the steps of:(a) irradiating the fabric with a beam ofmonochromatic light of given cross-sectional area sufficient toencompass a large number of warp and filling threads for developing fromsaid fabric a diffraction pattern having a central lobe and side lobes,(b) detecting at least a part of said diffraction pattern includingdetecting a predetermined number of said side lobes respectively by acorresponding number of linear arrays of photodetectors without usingany reference diffraction pattern, and (c) individually analyzing eachdetected side lobe itself by processing only the outputs of thephotodetector array corresponding to the respective detected side lobebeing analyzed to provide data indicative of the quality of said fabric,said side lobes being along axes oriented in directions normal to saidwarp and filling threads respectively, and wherein said processing stepincludes the steps of comparing the height and shapes of said side lobesto given references to provide at least a part of said output data. 2.The method of claim 1, in which one of said given references constitutesthe height and shape of said central lobe.
 3. The method of claim 2,including the step of comparing the height and shape of said centrallobe with a given standard to provide information indicative of majordefects in said fabric.
 4. The method of claim 1, in which at least someof said given references are provided from the mean value of a historyof amplitude and shape comparisons of said side lobes.
 5. The method ofclaim 1, in which said processing step includes the further steps ofcomparing the distance between centroids of the side lobes with givenreferences to determine spacing between warp threads and between fillingthreads of said fabric to thereby enable the number of warps per inchand enable the number of fillings per inch to be determined.
 6. A methodas in claim 1 including moving the fabric in a given plane and gradingthe fabric in accordance with the said data furnished by saidprocessing.
 7. The method of claim 6, including the step of individuallysequentially grading local areas of the fabric through which said beampasses.
 8. The method of claim 7, including the steps of totalling theindividual grades of local areas over a given large area of said fabricand assigning an overall grade to said large area as to quality based onsaid totalling.
 9. The method of claim 1, in which said large number ofwarps and fillings is at least 25 per inch.
 10. A method as in claim 1wherein step (c) includes analyzing at least the intensity of at leastone side lobe developed in said diffraction pattern.
 11. A method as inclaim 1 wherein step (c) includes analyzing at least the displacement ofat least one side lobe developed in said diffraction pattern.
 12. Amethod as in claim 1 wherein step (c) includes analyzing the intensityversus displacement relationship of at least one side lobe developed insaid diffraction pattern.
 13. A method as in claim 1 wherein said step(c) includes analyzing at least one side lobe relative to said centrallobe.
 14. A method as in claim 1 wherein said fabric is moved during atleast steps (a) and (b) and step (c) includes analyzing at least oneside lobe relative to said central lobe essentially independently ofchanges in transmissivity of said fabric due to its movement.
 15. Amethod as in claim 1 wherein said processing includes comparing thedistance between centroids of the side lobes with given references todetermine spacing between warp threads and between filling threads ofsaid fabric for determining the respective numbers of warps and fillingsper unit of measurement.
 16. A method as in claim 1 including moving thefabric in a given plane and wherein said step (c) includes comparing atleast one aspect of at least one current lobe with a recent history ofthat aspect of similar lobes.
 17. A method as in claim 16 wherein saidrecent history is a statistical history formed in an adaptive manner ofthe height and shapes of side lobes in the successive diffractionpatterns developed in said plane during movement of said fabric, thehistory for a current lobe comparison being continuously updated andrelated only to a predetermined number of immediately precedingdiffraction patterns.
 18. A method as in claim 17 wherein each said sidelobes of the respective pattern are related to develop a continuouslyupdated history which is independent of changes in transmissivity of thefabric during its movement.
 19. A method as in claim 1 wherein step (b)includes detecting at least one warp side lobe and at least one fillingside lobe in said predetermined number of side lobes and step (c)includes analyzing both said warp and filling lobes by processing theoutputs of the photodetector arrays for said warp and filling sidelobes.
 20. A method as in claim 19 wherein said step (b) includesdetecting said central lobe by a photodetector and step (c) includesanalyzing said central lobe by processing the output of saidphotodetector.
 21. A method as in claim 1 wherein the developeddiffraction pattern side lobes include two first order warp side lobesand two first order filling side lobes, all four of said warp andfilling side lobes being detected in step (b) and analyzed in step (c).22. A method as in claim 21 and further including detecting andanalyzing said central lobe.
 23. A method of automatically inspectingfabric comprised of warp and filling threads to determine the quality ofthe fabric, including the steps of:(a) irradiating the fabric with abeam of monochromatic light of given cross-sectional area sufficient toencompass a large number of warp and filling threads for developing fromsaid fabric a diffraction pattern having a central lobe and side lobes,(b) detecting at least part of said diffraction pattern includingdetecting a predetermined number of said side lobes by a respectiveplurality of linearly arrayed photodetectors without using any referencediffraction pattern, and (c) individually analyzing each detected sidelobe itself by processing only the outputs of that plurality ofphotodetectors employed in step (b) to detect the respective side lobebeing analyzed to provide data indicative of the quality of said fabric,said side lobes being along axes oriented in directions normal to saidwarp and filling threads respectively, and wherein said processing stepincludes the steps of comparing the height and shapes of said side lobesto given references to provide at least a part of said output data. 24.A method as in claim 23 including moving the fabric in a given plane andgrading the fabric in accordance with the said data furnished by saidprocessing.
 25. A method as in claim 23 wherein step (b) includesdetecting at least one warp side lobe and at least one filling side lobein said predetermined number of side lobes and step (c) includesanalyzing both said warp and filling lobes by processing the outputs ofthe photodetector arrays for said warp and filling side lobes.
 26. Amethod as in claim 25 wherein said step (b) includes detecting saidcentral lobe by a photodetector and step (c) includes analyzing saidcentral lobe by processing the output of said photodetector.
 27. Amethod as in claim 23 wherein the developed diffraction pattern sidelobes include two first order warp side lobes and two first orderfilling side lobes, all four of said warp and filling side lobes beingdetected in step (b) and analyzed in step (c).
 28. A method as in claim27 and further including detecting and analyzing said central lobe.